This application claims priority of Japanese Patent Application No. 2001-047077 filed in JPO on Feb. 22, 2001, the entire disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a device and a method to control gear shifting of a subtransmission. More particularly, the present invention relates to a device and a method suitable to control gear shifting of the subtransmission whose gear can be shifted to a high speed gear and a low speed gear. The subtransmission can be provided on a transfer of a four-wheel-drive vehicle.
2. Description of the Related Art
A transfer (a device for distributing drive force) of a four-wheel-drive vehicle is often provided with a subtransmission so as to enable gear shifting of the subtransmission between a high speed gear and a low speed gear. This gear shifting is carried out automatically by an actuator and a control unit. In this case, a switch is provided in a room of the vehicle, a driver can operate the switch in the room, and thereby the gear shifting of the subtransmission is automatically carried out.
In the meantime, this type of subtransmission generally does not include a synchronization mechanism. Furthermore, in the subtransmission, the gear rate of the low speed gear to the high speed gear is large, so that when the gear is changed from the high speed gear to the low speed gear, or from the low speed gear to the high speed gear in a state where the vehicle is running, mechanical damage can be caused. For these structural reasons, there are many cases in which the gear is prohibited from being shifted from the high speed gear to the low speed gear, or from the low speed gear to the high speed gear in the state where the vehicle is running, and only when the vehicle is standing, the gear shifting of the subtransmission can be carried out.
Conventionally, a speed of the vehicle is obtained from a pulse generated by a vehicle speed sensor, and the vehicle is assembled such that when the speed of the vehicle becomes zero or close to zero (this is called a substantially standing state), the gear shifting of the subtransmission becomes possible.
However, the vehicle speed sensor used for a speed indicator of a speedometer generates a pulse at intervals in accordance with the vehicle speed. When the vehicle speed becomes zero, the pulse is not generated, and when the vehicle is running at a considerable low speed close to zero, an interval between pulses is a greatly increased value. Therefore, accuracy in a vehicle speed detected by the vehicle speed sensor is considerably deteriorated. Although this deteriorated accuracy satisfies the speed indicator of the speedometer, the following problem occurs in a case where pulse data is used for judging whether or not the gear shifting of the subtransmission can be carried out.
In other words, an interval between pulses are detected, and this detected interval is converted into the vehicle speed. Accordingly, if after a certain pulse is generated, the next pulse is not generated, the vehicle speed cannot be calculated. However, when the vehicle is running at a very low speed (for example, 3 kilometers per hour), the interval between generation of a certain pulse and generation of the next pulse can be several seconds (for example, 3 seconds). Even if the driver operates the switch in order to carry out the gear shifting of the subtransmission during this interval, the gear shifting cannot be carried out unless the control unit waits for several seconds and recognizes that the vehicle speed is zero or near zero. As a result, the driver who operated the switch feels that something is wrong with this switching operation.
Furthermore, if the driver stops the vehicle by abruptly depressing a brake pedal during the interval between generation of a certain pulse and generation of the next pulse, the next pulse cannot be generated until the vehicle runs again. Therefore, a vehicle speed cannot be detected until the next pulse is generated. As a result, even if the driver operates the switch in order to carry out the gear shifting of the subtransmission during this period, the gear shifting cannot be carried out, so that a problem occurs.
In the meantime, there is one possible method for preventing this problem. In this method, the control unit judges that the vehicle speed is zero if a pulse is not detected within a predetermined period, and the gear shifting of the subtransmission can be carried out. However, in this method, also when a failure such as breaking of an electric line occurs and for this reason a pulse cannot be sent, the control unit judges that the vehicle speed is zero, so that there is a problem that the gear shifting can be carried out while the vehicle is running.
With the view of the above-mentioned problems, the present invention was made, and it is an object of the present invention to provide a device and a method for controlling gear shifting of a subtransmission. In this device and this method, a state where the vehicle is substantially standing is accurately recognized, the gear shifting of the subtransmission can be immediately carried out in a case where the vehicle is substantially standing, and it is possible to securely prevent the gear shifting during a state where the vehicle is running and there is a failure.
According to one aspect of the present invention, there is provided a device for, by using an actuator or a control unit, controlling gear shifting of a subtransmission which is installed on a vehicle and whose gear can be shifted only when the vehicle is substantially standing. This device includes vehicle speed pulse generating means for generating a vehicle speed pulse in accordance with a vehicle speed, first judging means for, without depending on the vehicle speed pulse, judging whether or not a first condition by which the vehicle can be considered to be running is satisfied, first timer means for counting a period of time for which the first condition is satisfied from the time each vehicle speed pulse is generated, first condition satisfied period determining means for determining a value of the period counted by the first timer mean to be a first condition satisfied period at the moment the satisfied first condition becomes unsatisfied, waiting period determining means for determining a waiting period in a predetermined manner by using the first condition satisfied period, second timer means for counting a period of time from the time the satisfied first condition becomes unsatisfied, and vehicle speed requirement accepting means for accepting the vehicle is standing or running at a very low speed or less when the period of time counted by the second timer means reaches the waiting period.
Preferably, the device further includes a switch which is manually operated so as to make a command to the effect that the gear shifting of the subtransmission should be carried out, and second judging means for judging whether or not a second condition by which the gear shifting of the subtransmission becomes possible is satisfied. This second condition includes a requirement that the vehicle should be standing or running at a very low speed or less. Preferably, when the switch is operated and switched, if the second condition is satisfied, the gear shifting of the subtransmission is carried out, and if the second condition is not satisfied, the gear shifting of the subtransmission is not carried out. Furthermore, when the switch is operated and switched, if the second condition is not satisfied, the gear shifting of the subtransmission is preferably not carried out even if the second condition becomes satisfied after the switch is operated and switched.
The first condition preferably includes a requirement that the vehicle should be running, and a requirement that a shift position of a main transmission is a position other than a neutral position and a parking position.
The second condition preferably further includes a requirement that an engine revolution speed should be equal to or less than a predetermined value, and a requirement that the shift position of the main transmission should be the neutral position or the parking position as well as the requirement that the vehicle should be standing or running at a very low speed or less.
Preferably, the waiting period is increased as the first condition satisfied period is increased, and an increase rate of the waiting period to the first condition satisfied period is changed to a larger value from a smaller value when the first condition satisfied period exceeds a predetermined threshold value. Further, the threshold value of the first condition satisfied period is preferably approximately a maximum period for which a signal (vehicle speed pulse) is awaited.
Preferably, at the moment the satisfied first condition becomes unsatisfied, the period counted by the first timer means is retained, and then if the unsatisfied first condition becomes satisfied, an additional count of the retained value is started.
The count of the first timer means is preferably cleared each time a vehicle speed pulse is generated.
The count of the first timer means is preferably cleared when an ignition switch is turned off.
The count of the first timer means is preferably cleared at the moment the gear shifting of the subtransmission is started or completed.
The subtransmission may be installed on a transfer of a four-wheel-drive vehicle.
According to another aspect of the present invention, there is provided a method of, by using an actuator and a control unit, controlling the gear shifting of the subtransmission which is installed on a vehicle and whose gear can be shifted only when the vehicle is substantially standing. In this method, a vehicle speed pulse is generated in accordance with a vehicle speed, and a first period of time for which a first condition, by which the vehicle can be considered to be running regardless of the vehicle speed pulse, is satisfied is counted from the time each vehicle speed pulse is generated. Moreover, in this method, when the satisfied first condition becomes unsatisfied, the first counted period of time is simultaneously determined to be a first condition satisfied period, a waiting period is determined in a predetermined manner by using the first condition satisfied period, a second period of time is counted from the time the satisfied first condition becomes unsatisfied, and it becomes possible to accept the vehicle is standing or running at a very low speed or less when the second counted period of time reaches the waiting period.
Additional objects, aspects, benefits and advantages of the present invention will become apparent to those skilled in the art to which the present invention pertains from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings.